In order to guarantee comfort of persons located within a closed zone (e.g., a lounge, conference room, or restaurant within a building), an air conditioner is used. The air conditioner is an equipment that enables persons to feel comfort and may be used as the same meaning as that of an air conditioning system. Two comforts such as thermal sensation and air quality may be provided by the air conditioner. Thermal sensation may be affected by weather and a peripheral environment. The air quality may be affected by a density or the number of persons (hereinafter, “occupants”) located within a corresponding zone, and in order to adjust the air quality, an Energy Recovery Ventilator (ERV) may be used. In this specification and claims, an “air conditioner” may perform a function of an ERV.